1. Field of the Invention
The present invention relates to navigation systems and, more specifically, to a navigation system constructed by a main device for carrying out navigation for a vehicle, and a sub-device for carrying out navigation for outside of the vehicle.
2. Description of the Background Art
An example of the above described navigation system is disclosed in U.S. Pat. No. 6,125,326 (and its corresponding Japanese Patent Laid-Open Publication No. 10-103999 (1998-103999)). Such conventional navigation system is constructed by a main device fixedly incorporated in a vehicle and a sub-device removably mounted on the vehicle. When mounted on the vehicle, the sub-device displays cartographic information and current position information on a main display under the control of a control unit. Before removed, the sub-device receives, from the control unit, a transfer of cartographic information about a predetermined area surrounding the current position of the vehicle. After removed, the sub-device displays a map based on the cartographic information transferred from the control unit and the current position of the user traveling outside of the vehicle.
However, the conventional navigation system is not so convenient for users to use. To describe this more specifically, consider a case where a user goes from a starting point by vehicle, gets off the vehicle at some point, and then goes to a destination point on foot. In this case, the user first uses the main device while driving the vehicle, and then uses the sub-device after getting off the vehicle. In the conventional navigation system, however, as described above, only the cartographic data for the surrounding area has been transferred to the sub-device. Consequently, the user has to further input information about the destination point in the sub-device for receiving route guidance, which is quite burdensome.